Ultra-narrow bandwidth single-photon sources operating at room temperature are of vital importance for viable optical quantum technologies at scale, including quantum key distribution, cloud-based quantum information processing networks, and quantum metrology. Here we show a room-temperature single-photon source generating polarised photons at a rate of 5MHz based on an inorganic CsPbI3 perovskite quantum dot embedded in a tunable open optical microcavity. When coupled to the mode of the

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... cavity, the quantum dot room-temperature emission becomes single-mode and the spectrum narrows down to just ∼ 1 nm. The excellent directionality of the optical modes enables high single-mode collection at RT, offering promising performance for photonic and quantum technology applications. We measure 94% single-photon purity under pulsed and continuous-wave (CW) excitation.